The present invention relates generally to plasma arc torches and, in particular, to connection designs for interconnecting an electrode in a plasma arc torch in electrical connection with the cathode of the torch.
Plasma torches, also known as electric arc torches, are commonly used for cutting and welding metal workpieces by directing a plasma consisting of ionized gas particles toward the workpiece. In a typical plasma torch, a gas to be ionized is supplied to a lower end of the torch and flows past an electrode before exiting through an orifice in the torch tip. The electrode, which is a consumable part, has a relatively negative potential and operates as a cathode. The torch tip (nozzle) surrounds the electrode at the lower end of the torch in spaced relationship with the electrode and constitutes a relatively positive potential anode. When a sufficiently high voltage is applied to the electrode, an arc is caused to jump the gap between the electrode and the torch tip, thereby heating the gas and causing it to ionize. The ionized gas in the gap is blown out of the torch and appears as a arc that extends externally off the tip. As the head or lower end of the torch is moved to a position close to the workpiece, the arc jumps or transfers from the torch tip to the workpiece because the impedance of the workpiece to ground is lower than the impedance of the torch tip to ground. During this "transferred arc" operation, the workpiece itself serves as the anode.
In a conventional plasma torch, an electrode having external threads engages an internally threaded bore in a cathode body to secure the electrode to the torch head. However, it is expensive to manufacture a threaded electrode and cathode. It is also often time consuming to perform a threading operation on consumable items such as electrodes, particularly because a separate tool, such as a wrench, must be used to install the electrode in or remove it from the cathode. In another torch design, the electrode is held in electrical contact with the cathode using a nozzle and shield cup. When the shield cup is tightened on the torch body, the electrode and nozzle are secured in fixed position on the torch, with the electrode held in electrical contact with the cathode. Assembly of this type of torch, such as when the consumable electrode or nozzle needs replacing, is often cumbersome because if the torch is not held upright during assembly the electrode will simply fall out of or may be easily jarred from the torch. This is particularly problematic when the torch operator performs the assembly at a location, such as up on a ladder or scaffolding, from which retrieval of a dropped electrode is inconvenient and can result in loss of the electrode.
There is a need, therefore, for a plasma torch having a threadless design for electrically connecting an electrode to a cathode in the torch to inhibit axial movement of the electrode outward from the torch during assembly of the torch.